1. Field of the Invention
The present invention relates to a manufacturing method of a hermetic container and, more particularly, to a manufacturing method of a hermetic container for an image display apparatus having electron-emitting devices in each of which an inside is held in a vacuum state and a phosphor film.
2. Description of the Related Art
Image display apparatuses of a flat panel type such as organic LED display (OLED), field emission display (FED), plasma display panel (PDP), and the like are well known. Each of those image display apparatuses is manufactured by forming an internal space by sealing glass substrates which face each other and has a container in which the internal space is partitioned to an external space. To manufacture such a hermetic container, a spacing distance defining member, a local adhesive, and the like are arranged between the facing glass substrates as necessary, a sealing material is arranged in a frame shape to peripheral portions of the glass substrates, and a heat sealing process is executed. As a heating method of the sealing material, a method whereby the whole glass substrates are baked by a furnace and a method whereby the sealing material is selectively heated and molten by local heating have been known. The local heating is more advantageous than the whole heating from viewpoints of a time which is required to heat and cool, an energy which is required to heat, productivity, a prevention of thermal deformation of the hermetic container, a prevention of thermal deterioration of a function device arranged in the hermetic container, and the like. Particularly, a unit using a laser beam has been known as a unit for performing the local heating (local heating unit). Such a manufacturing method of the hermetic container can be also applied as a manufacturing method of a hermetic container (vacuum insulated grazing glass) which does not have a function device therein.
A seal-sealing method of a container which is used for an FED, a fluorescent electron tube (VFD), and the like has been disclosed in Japanese Patent Application Laid-Open No. H08-022767. First, a first glass substrate and a second glass substrate are position-matched through a sealing material (seal glass). Subsequently, the circumferential sealing material (seal glass) is locally heated by the local heating unit and the first glass substrate and the second glass substrate are temporarily fixed in at least two positions. After that, by heating them in a seal-sealing furnace, the first glass substrate and the second glass substrate are seal-sealed.
A manufacturing method of a container of an FED has been disclosed in U.S. Pat. No. 6,109,994. First, a frame member and a sealing material (frit) are arranged in circumferential edge portions of the first glass substrate and the second glass substrate arranged so as to face each other. The sealing material has venting slots for exhaustion. Subsequently, a laser beam is intermittently irradiated along the extending direction of the sealing material, the sealing material is discretely heated, and discrete portions are sealed. Subsequently, the laser beam is continuously irradiated to the whole circumference of the sealing material including partially sealed regions, and while embedding the venting slots between both of the glass substrates by thermally expanding the sealing material, the internal space is airtightly sealed.
A manufacturing method of a hermetic container has been disclosed in Japanese Patent Application Laid-Open No. 2009-070687. A sealing material is arranged in a gap portion between a first glass substrate and a second glass substrate and the sealing material is partially heated by a heating apparatus along the extending direction of the sealing material and is also pressurized. A pressurizing force of the sealing material is changed based on a height of sealing material at a heating position.
According to the methods in the related arts, there is a case where adherence between the sealing material and the glass substrate when the laser beam is irradiated is difficult to be assured due to an influence of the rough surfaces of the sealing material and the glass substrates or an influence of the rough surfaces which are caused by structures such as wirings and the like provided for the glass substrates. When the adherence deteriorates, there is a case where airtightness of the hermetic container deteriorates and the reliability is deteriorated.
FIG. 6A illustrates a state where a height of sealing material 901 for sealing two glass substrates 912 and 913 constituting a hermetic container is variable. FIG. 6B illustrates a state where wirings 920 for supplying an electric power to an inside of the hermetic container are arranged between the first glass substrate 912 and the second glass substrate 913. As illustrated in FIGS. 6A and 6B, in the case where the sealing material 901 is locally heated and molten in a state where it is difficult to assure adherence between the sealing material 901 and the glass substrates 912 and 913, a leveling action of the sealing material is inferior to that in the case where the sealing material 901 is heated as a whole. Thus, it is liable to become a cause of a defective junction and cracks. It is, therefore, important that the adherence between the sealing material and the glass substrates is assured over the whole circumference of the sealing material during a step of irradiating a laser beam as a local heating unit and heating and melting the sealing material.
It is an object of the present invention to provide a manufacturing method of a hermetic container whereby adherence between a sealing material and glass substrates is assured and airtightness is improved.